Why low-carb diets are not the best solution

For much of the last generation, carbohydrates have been demonized as the main culprit behind unnecessary weight gain by proponents of fad dieting. Their basis is the tired, antiquated carbohydrate-insulin obesity model – which assumes that hyperinsulinemia leads to a surplus of calories in fat cells overriding lean tissue metabolism.  In the last few years, Dr. Kevin D. Hall and researchers at the NIH have flipped these theories upside down using studies that measuring the weight loss of subjects who experimented with isocaloric diets restricting both carbohydrates and fats. Hall and his associates found that while the reduced carb groups (RC) lowered RER and insulin as expected, it was the reduced fat (RF) who lost more body fat and maintained a higher metabolism (total daily energy expenditure).

In a follow up study over a longer term, subjects tried more extreme versions of each diet (RC and RF) while being permitted to consume as many calories as they needed.  Once again, the RF group had much higher levels of glucose and insulin, but ended up consuming 700 kcal/day less than the RC group (every single subject ate less when on the reduced fat diet vs the reduced carb diet) and dropping more bodyweight and fat.  The same research confirmed that long-term low-carb dieters (10% or less from CHO) have quickly gone into a state of ketosis, where the body uses it’s amino acids (muscle) for gluconeogenesis (energy), resulting in a decreased nitrogen balance (muscle loss).

Dr. Hall and his team also performed a research review of over 30 similar studies experimenting with CHO and fat restriction, and their findings reaffirmed that diets reducing fat instead of carbohydrates maintained a higher energy expenditure (~150 calories per day) with greater losses in body fat.  One must remember that in addition to its role in maintaining a healthy skeletal frame, muscle is more metabolically active and burns more calories.

In summary, it can be concluded that patients who already have type 2 diabetes can benefit from low carb diets that help keep insulin levels controlled, whereas other people who are overweight or obese should instead focus on reducing fat and highly-processed food from their diets; while remembering that carbohydrates have their place in promoting high levels of metabolic energy, preventing nutritional deficiencies, and promoting healthy brain function.                                                      

– CHRIS BORGARD

Sources:

1. KD Hall et al. Cell Metabolism. 22: 427-436 (2015).
2. Hall & Guo; Gastroenterology. 152: 1718-27 (2017).